1. Technical Field
The present invention relates to printed circuit boards. In particular, it relates to a method and apparatus for rapidly and inexpensively fabricating printed circuit boards using general purpose equipment such as a personal computer with an ordinary laser printer and without requiring any special equipment.
2. Background Art
The manufacture of printed circuit boards has traditionally involved special equipment. For example, a typical development process includes the steps of designing the land pattern for the circuit board, using the design to create a mask, manufacturing a printed circuit substrate with a surface conductive layer such as copper, coating the copper layer with a photoresist material, exposing the photoresist while masked, and etching the board to remove the copper in areas not masked. This procedure is not inconvenient during the mass production phase of a circuit.
On the other hand, the development of electronic circuitry has traditionally involved the fabrication of a small number of prototype boards to allow new circuit designs to be tested prior to entering the mass production stage. As a result, the special equipment and procedures required by the masking process often result in extended time delays since the board designs must be sent out from the design department to the department or outside company which has the specialized equipment. The time delays result in higher costs and delays in bringing products to market.
The prior art has made attempts to eliminate the need to use outside resources to fabricate test boards. For example, one known solution uses a special purpose printer to fabricate printed circuit boards with a personal computer. This approach uses a printer with a special solder ribbon. The computer deposits the solder directly onto a copper sheet. After the circuit design is printed onto the copper sheet in this manner, the solder acts as the mask during the etching step. While this method improves the turnaround time required to fabricate a board as compared to sending the board out for fabrication outside the department, the cost of fabricating boards in this manner is expensive due to the cost of the specialized printer and the solder ribbons. In addition, since the equipment is specialized in nature, there may be queuing delays if several individuals are waiting to access the printer at the same time.
A similar approach was used in the development of direct metal transfer to a substrate material. This approach eliminated the solder ribbon, but replaced it with a metal resistive ribbon which is selectively heated and brought into contact with the substrate to directly apply the circuit land pattern. As was the case in the foregoing example, this method requires special equipment which results in increased cost and potential queuing delays.
More recently, attempts have been made to use common equipment, such as the laser printer on an ordinary personal computer. A significant advantage of this approach is reduced cost since the printer will be available for other business tasks and not lay dormant when circuit boards are not required. One known method has been the use of laser printers to produce a mirror image of the land pattern on paper. The paper is then held in contact with the substrate and reheated. When the paper is sufficiently heated, the toner remelts and adheres to the substrate. This method eliminates the need for a special printer and is an improvement over the aforementioned prior art approaches. However, it does not eliminate the need for special equipment. To remelt the toner, a heater is required which adds to cost. In addition, the heater adds a new issue of safety due to the high temperature required to remelt the solder. A third drawback to this method is the degradation in precision each time the toner is melted. In circuit designs having finely drawn land patterns, breaks in the land pattern may result due to the second toner melt which may result ultimately in circuit failure. A fourth drawback to this method is that the paper actually fuses to the substrate along with the toner. As a result, the circuit board must be soaked in water to dissolve the paper after the second toner melting is complete. A design disadvantage to this method also occurs due to the fact that since the printed side of the paper must be placed against the substrate, the circuit must be printed in mirror image to allow the toner to be deposited correctly. Finally, this method also requires care and skill on the part of the user since successful toner transfer depends on precise control of three variables: heat, pressure, and time. As a result, misjudgment of any of these variables may result in defective boards and the further expense of duplicated effort to create a second or third board.
Another method, similar to the one discussed in the previous paragraph, uses a multilayer sheet which has a paper backing. In this method, the circuit is printed onto the non-paper portion of the sheet. The paper backing is peeled away and the sheet is placed in contact with the substrate. The sheet is then heated to remelt the toner. As was the case above, the toner is melted twice, which results in diminished resolution. Likewise, the image must be designed in reverse so that the land pattern will be formatted correctly after the second melt. The principle advantage of this method over the previously discussed method is that the sheet can be peeled from the substrate and does not have to be soaked in water.
While addressing various aspects of fabricating printed circuit boards, the prior art has typically provided solutions which require expensive special purpose equipment, require multiple toner melting steps with the resulting decrease in quality, require circuits to be designed in reverse image due to the multiple melting steps, and may not be capable of providing land patterns on both sides of a printed circuit board. The prior art has not provided a method of fabricating circuit boards which can be rapidly and easily designed, fabricated in-house with general purpose computer equipment, fabricated with a direct deposit of toner onto the conductive sheet, and not require heating equipment or multiple toner melting steps.